Apparatus and method for starting a vapor generating power plant



J 1.965 E. KOCHEY, JR 3,189,006

APPARATUS AND METHOD FOR STARTING A VAPOR GENERATING POWER PLANT FiledNov 20 1962 .Y 2 m W m B ML A m F D m w D E m B Z 5 .F 6 M llllll ll 9 60 3 6 United States Patent 3,189,006 APPARATUS AND METHOD FOR STARTING AVAPOR GENERATlNG POWER PLANT Edward L. Kochey, Jr., Colebrook, Conm,assignor to Combustion Engineering, Inc, Windsor, Conn, a corporation ofDelaware Filed Nov. 20, 1962, Ser. No. 238,885

8 Claims. (Cl. 122406) The invention relates in general to a forced flowoncethrough vapor generating power plant, and more particularly to animproved apparatus and method for starting operation of the vapor, forinstance, steam generator and turbine associated therewith.

It is known when starting up a forced flow oncethrough vapor generator.to separate the vapor superheating and turbine portion from the vaporgenerating port-ion by a so called boiler throttling valve. Suchseparation permits the use of auxiliary vapor in the superheater portionfor the. purpose of starting up the turbine, while the vapor generatingportion at the same time is brought up to the desired temperature andpressure; or in other instances the fluid in the vapor generatingportion after having been raised to a high pressure and temperature canbe expanded through the boiler throttling valve to form a vapor andliquid mixture at lower pressure, with such vapor, after having beenseparated from the liquid in .a vapor and liquid separator andsuperheated, then being used for starting up and rolling the turbine; orin still other instances, the temperature of the high pressure fluid canbe raised to such a value that only dry vapor is produced when the fluidis expanded through the boiler throttling valve to the lower pressure,with such vapor then being superheated and utilized to heat and roll theturbine.

In employing these above-mentioned procedures, however, costlyadditional apparatus is required including vapor and liquid separatingvessel and associated valves and piping, which equipment is only beingused during start up and shut down operating periods. The considerableinvestment represented by this equipment is therefore not economicallyemployed. Furthermore, during an initial phase of the start upprocedures as hereinabove described, a turbine by-pass line mustgenerally be made use of, such line leading from a point between thesuperheater and the turbine shut-off valve to a low pressure region, forinstance the hot well of the condenser.

While the present invention still makes use of the boiler throttlingvalve, it discloses an improved apparatus and method for starting aforced flow once-through vapor genorator which does not require start upapparatus such as separating vessel with associated valves and iping,nor does it make use of a turbine by-pass for raising the temperature ofthe vapor to a temperature suitable for rolling the turbine.

The objects of the present invention accordingly include an improvedapparatus and method for starting a vapor generator of the forced flowonce-through type with only vapor entering the finishing superheater;with such object being obtained without the use of auxiliary vapor forstarting the turbine; without the use of a separating bottle or vesseland associated valves and piping; without the necessity of providing aturbine bypass for starting up purposes; and without the requirement ofadhering closely to given pressure and temperature conditions in thevapor generating portion before the high pressure fluid in said portioncanbe expanded to the lower pressure prevailing in the vapor heatingportion of the vapor generator, so that only vapor is produced therein.

Other objects and advantages will become apparent as the description ofillustrative embodiments of the invention proceeds. The novel featureswhich are considered characteristic of the invention are set forth withparticu- 3,1893% Patented June 15, 1965 larity in the appended claims.These claims as well as the following description of the invention willbest be understood when read in conjunction with the accompanyingdrawing in which:

FIG. 1 is a representation of a vapor power plant system in the form ofa flow diagram incorporating one em: bodiment of the present inventionas characterized by pressure differential means being provided tormaintaining the liquid level in the convection superheater at a desiredelevation.

'FIG. 2 is a diagrammatic illustration of the pressure indicating meansin the form of diaphragms.

FIG. 3 is a portion of a vapor power plant similar to that illustratedin FIG. 1, however, including mechanical means for indicating the liquidlevel in the convection superheater and maintaining said level at adesired location.

Referring now to the drawing in which like reference characters are usedthroughout to designate like elements the diagrammatic representation ofFIG. 1 discloses a forced flow one-through vapor generator 10. A feedpump 12 is organized to supply Working fluid to vapor generator 19 froma working fluid source 14 by way of conduit 16. To control or shut-oil?the flow of working fluid a feed valve 18 is provided in conduit 16. Theworking fluid passes serially through economizer 2t), conduit-s 21 and22, vapor generating tubes 24 lining the wall-s of furnace chamber 25,tubes as, header 23, conduit 39, convection superheater 32, conduit 34,finishing vapor superheater 36 and conduit 38, to a point of use such asvapor turbine 40. A valve 42 is provided in conduit 38 to shut ofl theflow of the working fluid to turbine 40. After having given up the majorportion of its thermal energy in turbine 44] the working fluid vapor iscondensed in condenser 14 and returned to the vapor generator via feedpump 12.

Fuel and air for combustion are supplied to vapor generator It) by wayof burner 44 in any conventional manner. The hot combustion gasesproduced by the burning of the -fuel pass in heat exchange relation overthe heat absorbing surfaces of the vapor generating tubes 24, finalsuperheater 36, convection superheater 32 and economizer 20- To maintaina minimum safe velocity in the vapor generating tubes 24 during .startup and low load operation a recirculating circuit 46 is provided forreturning a port-ion of the fluid that is leaving header 28 for passageto convection superheater 32 through conduit 30, to the inlet of vaporgenerating tubes 24 by way of mixing vessel 48 and recirculating pump50. A valve 52 permits control or stoppage of the flow of fluidrecirculating through circuit t6. As an alternative to recirculationduring start-up or low load operation, excess fluid can be discharged towaste through drain line 54 for the purpose of maintaining a minimumvelocity in furnace tubes 24. To control flow through conduit 54 aboiler extraction valve 55 is provided.

As earlier mentioned hereinabove it has been found of advantage instarting up once-through vapor generators to make use of a shut-oft andthrottling device for separating the vapor generating portion 25 from.the vapor superheating portion 32 and 36. In practice this devicecomprises a shut-off valve 56 and a throttling valve 57 arranged inbypass relation with valve 56. The purpose of bypass valve 57 is toobtain throttling with high pressure drop and small flow quantities,while the main shut-off valve 56 is designed for relatively low pressuredrops and large flow quantities.

By employing boiler throttling valves 56 and 57 it is possible tocommence start-up operation of the superheating and turbine portionwithout much delay after the startup procedure for the vapor generatingportion has begun. To accomplish this, however, superheated vapor mustbe furnished to the turbine by the finishing superheater 36 long beforesuch vapor could be produced by the vapor generating tubes 24 at normaloperating pressure and tempera-ture. Furthermore, while a large amountof heated gases are released in furnace chamber 25 for bringing theoperating fluid up to operating pressure and temperature,

the radiant heating surface of finishing superheater 36 must beprotected from the heat of these gases during the final period ofthestart-up operation ofthe vapor generating section. Since it isundesirable to utilize operating fluid in the liquid state for thispurpose vapor must be available for cooling the finishing superheater 36long beforethe vapor. generator is capable of furnishing such vapor atnormal operating temperature and pressure.

In accordance with the invention this is accomplished f by operating theprimary or convection superheater 32 as a vapor generator, producingvapor at a pressure initially considerably lower than the pressurenormally at,-

tained in the vapor generating portion 24 ofthe gen erator. I c Tomaintain a desired'liquid level 58 in the convection superheater 32 whenoperating it as a vapor gen- V finishing superheater 36 for "for beingsuperheated therein.

cooling the tubes thereof and After a suitable pressure and temperaturehas been reached in conduit 38 as indicated by pressure sensing device74 and temperature sensing device 76 valve 42 is being opened to admitsuperheated vapor to turbine 40 l for rolling and heatingiof the same. av

q As the liquid in convection superheater 32 is being evaporated,superheated and conducted to the turbine additional. fluid is beingadmitted by'way of valve 57 .in response to a lowering of the liquidlevel 58. As

earlier described herein this can be accomplished by the pressuredifferential indicating device 60 receiving pressure impulses throughdiaphragms 64 and 66 as illustratively shown in FIG; 2, or receiving anindication of the liquid level elevation by'means of float 68 and leversystom 65? as shown in FIG. 3. I

7 With turbine. 40 thus being provided with a source of superheatedvapor, while the temperature of the fluid in'the, vapor generatingportion is being ,raised to the normal temperature necessary forgeneration of vapor,

tion superheater 32 can be allowed to evaporate.

a'point in thestart-u'p operation of the unit will eventually be reachedwhen all of the liquid in the convec- The temporary function ofsuperheater 32 of evaporating liq uid is thereby gradually replaced bythenormal function 67 and float 68 are shown for indicating theliquidlevel' 58 and for conveying such indications to transmitter 70. Otherconventional apparatus, for indicating the location of the liquid levelmay housed in connection with the present invention.

According to the invention the start-up operationiof' the vaporgenerator includes the following steps:

With valves 56 and 57 closed, working fluid is pumped through economizer20 and furnace tubes 24 and dis charged through conduit 54 to a point oflower pressure.

ing the'heating of the fluid in tubes 24 recirculation of fluidisestablished through these tubes bymeans of re-,

circulating pump 50, with the recirculated flow being such that aminimum safe velocity is always maintained in,

tubes 24. Obviously, but in a less economical manner such safe velocitycould also be maintained by discharging a suificient quantity. of theWorking fluid byway of conduit 54 and valve 55. a V, a

The above mentioned predetermined fluid temperature measured atpoint 72usually correspondsto atempera-i ture of the combustion gases flowingover finishing superheater 36 at which it becomes unsafe to operate-theunit without flowing a cooling medium such as vapor through the tubularheating surface of "finishing superheater-36.

57 is gradually beingwopened permitting high pressure fluid to flow intoconvection superheater' 32, with tur g bine valve 42 controlled tomaintain a desired lower pressure therein. Pressure indicating devices73 are provided to show the pressure drop across valves 56 and57.

Because of the lower pressure prevailing in superheater 32 and 36 aportion of the high pressure fluid flashes into vapor with'the remainingliquid establishing a liquid level 58. Convection superheater32accordingly now operates as a vapor generator absorbing heat from thecombustion gases flowing thereover. The saturated'vapor thus produced byflashing and evaporation flows into ing point.

After this so-called clean-up operation, valve 55 1 is closed or set toopen at a predetermined high pres- Accordingly, at this point oftheoperating procedure valve thereof of superheatingithe vapor. in vaporgenerating portion 25 increases, a greater pro- As] the temperatureportion of vapor is being produced by flashing, with the liquid levelinsuperheater 32 receding to the vanishing point. Or, as the pressuresin'vapor generating portion 25 and superheating portions 32 and 36approach equality, less and less of the total vapor is'being produced byflashing and moreand. more by evaporation in tubes 24 as the liquidlevel in superheater 32 recedes to the vanish- As soon as substantiallyequal pressures are established ,across valves 56 and 57 as'observedbypressure sensing device 73 these valves will be fully opened and thevapor generator operated under normal operating conditions and control.V The present invention of amethod and apparatus for starting up, aonce-through vapor generating power plant accordingly offersthe'following important advantages:

While heretofore it was deemed desirable if not essential toemploy a'vapor and liquidseparating vessel with associated-valves and pipingbetween the boiler throttle valves 56,57 and superheaters 32,136, suchauxiliary equipment is not required when starting up a once-throughvapor generator in accordance with the teaching of the presentinvention. v

While some start-up procedures as heretofore practiced required inlieuof a vapor and liquid separating vessel the adhering to very criticalconditions of pressure and temperature of the fluid in the vaporgenerating section 25, before this fluid could be expanded through theboilerthrottling valve 56, 57 so that only dry steam would result fromsuch expansion, the present invention does not require adherence to suchcritical conditions of pressure and temperature. 7 c

Whilein the majority of start-up procedures ofoncethrough forced flowvapor generators the use of a turbine by-pass is' a dominating featureessential for successfubstart-up of the power plant, such turbineby-pass can be eliminated when starting up a power plant of theabove-named type in "accordance with the present invention.

, While specific embodiments of the invention havebeen shown anddescribed herein, it will be apparent to those skilled in the art thatvarious changes, specifications, substitutions, additions and omissionsmay be made without departing from the spiritand scope of the inventionas set forth in the appended claims.

What I claim is:

1. A method of starting a forced flow once-through vapor generatorhaving a first heating section including vapor generating furnace wallsand having a second heating section including a primary superheater anda finishing superheater said heating sections being directly connectedand being serially arranged for flow of a vaporizable fluidtherethrough; said method comprising the following steps:

(1) maintaining a body of heated working fluid at a predeterminedrelatively high pressure in said first heating section;

(2) flowing working fluid from said first heating section directly tosaid primary superheater, while reducing the pressure thereof from saidhigh pressure down to a predetermined low pressure maintained in saidprimary superheater said low pressure being such that a partial flashingof said fluid into vapor occurs, so as to obtain a body of vaporizablefluid and a body of vapor, and establish a fluid level in said primarysuperheater;

(3) generating additional vapor from said body of vaporizable fluid insaid primary superheater and passing vapor to said finishing superheaterfor superheating therein;

(4) conducting said superheated vapor to a point of use; and

(5) controlling the fiow of vaporizable fluid from said first heatingsection to said primary superheater to establish and maintain the fluidlevel in said primary superheater within desired limits.

2. A method of starting up a forced flow once-through steam generatorhaving a tubular first heating section and having a tubular secondheating section including a primary superheater and a finishingsuperheater said heating sections being directly connected and beingserially arranged for flow of water and steam therethrough; said methodcomprising the following steps:

(1) producing and maintaining a body of heated water at a predetermined'supercritical pressure in said first heating section only;

(2) flowing water from said first heating section directly to saidprimary superheater, while throttling it from said supercriticalpressure down to a predetermined subcritical pressure maintained in saidprimary superheater and finishing superheater, said subcritical pressurebeing such that a partial flashing of water into steam occurs, so as toobtain water and steam in said primary superheater and steam only insaid finishing superheater;

(3) generating additional steam from said water in said primarysuperheater. and passing steam to said finishing superheaters forsuperheating therein;

(4) conducting said superheated steam to a point of use; and

(5) controlling the flow of water from said first heating section tosaid primary superheater to establish and maintain a water level in saidprimary superheater within desired limits, while the steam generated insaid primary superheater passes to said finishing superheater and tosaid point of use.

3. A method of starting up a forced flow once-through vapor generatorhaving a first heating section including vapor generating furnace wallsand having a second heating section including a primary superheater anda finishing superheater said heating sections being directly connectedand being serially arranged for flow of a vaporizable fluidtherethrough; said method comprising the following steps;

(1) maintaining a body of heated working fluid at a predeterminedrelatively high pressure in said first heating section;

(2) recirculating said body of heated working fluid from the outlet ofsaid furnace walls directly to the inlet thereof;

(3) flowing working fluid from said first heating section directly tosaid primary superheater, while reducing the pressure thereof from saidhigh pressure down to a predetermined low pressure maintained in saidprimary superheater said low pressure being such that a partial flashingof said fluid into vapor occurs, so as to obtain a body of vaporizablefluid and a body of vapor, and establish a fluid level in said primarysuperheater;

(4) generating additional vapor in said primary superheater and passingvapor to said finishing superheater for superheating therein;

(5) conducting said superheated vapor to a point of use; and

(6) controlling the flow of vaporizable fluid from said first heatingsection to said primary superheater to 1 establish and maintain thefluid level in said primary superheater within desired limits.

4. A method of starting up a forced flow modified oncethrough vaporgenerator having a first heating section including vapor generatingfurnace walls and having a second heating section including a primarysuperheater and a finishing superheater said heating sections beingdirectly connected and being serially arranged for flow of a vaporizablefluid therethrough; the invention comprising feeding vaporizable fluidto said first heating section only; heating said vaporizable fluid bysupplying heat to said first and second heating sections; permitting afirst overflow of heated vaporizable fluid from said first heatingsection to a point of lower pressure for fluid cleanup purposes;discontinuing the feeding of vaporizable fluid to said first sectionwhile recirculating said fluid from the outlet of said furnace wallsdirectly to the inlet thereof to maintain the flow velocity in saidfurnace walls above a predetermined minimum velocity; discontinuing saidfirst overflow and raising the pressure in said first heating section toa predetermined value in excess of that prevailing in said secondheating section; permitting a second overflow from the relatively highpressure region of said furnace walls to the relatively low pressureregion of said primary superheater said excess of pressure being suchthat a partial flashing of said fluid into vapor occurs, so as to obtaina body of vapor and a body of vaporizable fluid in said primarysuperheater and to establish a liquid level therein; generating vaporfrom said body of vaporizable fluid in said primary superheater andflowing said vapor from said primary superheater to said finishing forsuperheating therein; conducting said superheated vapor to a point ofuse; and re-establishing a controlled flow of vaporizable fluid to saidsteam gtfenerator consistent with the flow of vapor to said point 0 use.

'5. In a forced flow once-through vapor generator having a first heatingsection and having a second heating section including a primarysuperheater having a bottom inlet and a top outlet and a finishingsuperheater said heating sections being directly connected and beingserially arranged for flow of a vaporizable fluid therethrough; thecombination comprising:

( 1) means for maintaining a body of heated vaporizable fluid at apredetermined relatively high pressure in said first heating section;

(2) means for flowing water from said first heating section directly tothe bottom inlet of said primary superheater;

(3) means for throttling said fluid from said high pressure down to arelatively low pressure maintained in said primary superheater with saidlow pressure being such that a partial flashing of said fluid into vaporoccurs, so as to obtain vapor and liquid and establish a liquid level insaid primary superheater;

(4) means for generating vapor in said primary superheater;

(5) means for passing vapor from the top inlet of said primarysuperheater to; said finishing 'superheater;

(6) means for superheating said vapor; (7) means for conducting saidsuperheated vapor to a point of use; .s

(8) means for controlling'the flow of fluid from first heating sectiontosaid primary superheater' so as to establish and maintain the liquidlevel in said 'pri mary'superheater within desired limits; and

(9) means for feeding vaporizable fluid to said first heating section inconformity with the flow of superheated vapor to said point of use.

6. ,In a forced flow modified'once-through steam generator having afirst heating section including steam generating furnace walls andhaving a second heating section including aprimary superheater and afinishing superi said waterby supplying a heating medium to said steamgenerator in heat exchange relation with the heating surfaces thereofincluding said furnace walls, a primary superheater and finishingsuperheater; relief valves means for limiting the pressure in said firstheating section to a predetermined value and for permitting a firstoverflow ofheated water'due to expansionvthefreoffrom said first heatingsection to a point of lower pressure; shut-off means for discontinuing'the feeding of water to said first. section; means for recirculatingsaid water from a point downstream of the outlet of saidfurnace walls tothe inlet thereof to maintain atpredetermi ned minimum flow velocity insaid furnace walls;'s hut-'oif means for discontinuing said; first.overflow;'throttling means for heater said heating sections beingdirectly connected and 7 beingserially arranged for flow of water andsteam there through; the combination comprising: s means for maintaininga body of'heated water at a predetermined supercritical pressure insaid'first heat,- ing section; 1

means for recirculating heated Water from the putlet' of said furnacewalls directly to the inlet thereof; smeans for flowing water fromsaid'first heating section directly to said primary superheater;

means, for throttling said water from sald supercritical pressuredown'to the subcritical pressure maintained in said primarysuperheatersaid low pressure being such that a partial flashing ofwater'into steam occurs, a so as to obtain waterand steam and establisha water 7 level in said primary superheater; means for generating steamin said primary superheater; meansfor passing steam to'said finishingsuperheater; 7 means for superheatingfsaid steam; r means for conductingsaid superheated steam to a point of use; I i

means for controlling the flow of water from said first heating sectionto said primary superheater so as to establish and maintain the waterlevel in said primary superheater within desired limits; and V 7 meansfor feeding water to said body of water in conformity with the flow ofsuperheated steam to said point of use. 7. In a forced flow modifiedonce-through steam generator having a first, heating section" includingsteam. generating furnace walls, and having a second heating sectionincluding aprimary superheater and a finishing superheater, said heatingsections being serially arranged for flow of water and steamtherethrough; the combination comprising valve means for shutting oifflow from i said first to said second heating section; means for feedingwater to said first heating section; means for heating means forcontrolling saidflow'into said primary superheater such as to maintainsaid water 'level at a desired elevation; means for superheating thesteam received from said primary superheater in said finishingsuperheater and conduct it to a point of use; and meansforre-establishing a flow of feedwater to said steam generator consistentwith the flow of steam to said point of use.

8. The organization defined in-claim 7 wherein said means for indicatingthe water level in said primary superheater and for maintaining the sameat a desired elevation comprises means for obtaining'a static pressuredifferential between the inlet and the outlet of said primarysuperheater and means for. regulating the flow from said first heatingsection to said primary superheater in response to variations in saidpressure differential.

References Cited by the Examiner UNITED STATES PATENTS 1,767,714 6/30Stender 122-406 3,019,774 2 /62 Beyerlein.

OTHER REFERENCES Strohmeyer: Large Sub and SupercriticaI Steam GeneratorStartup and Control System Integration With The Turbine Generator,reprint of paper presented at American Power Conference, Marchv 1962.;FIGS. 5 and 7 and pages 6-10 in'particular.

PERCY L; PATRICK, Primary Examiner. MEYER PERLIN, Examiner.

UNITED STATES PATENT OFFHHZ CERTIFICATE OF CORRECTION Patent No.3,189,006 June 15, 1965 Edward L. Kochey, Jr.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6, line 50, after "finishing" insert superheater Signed andsealed this 30th day of November 1965.

(SEAL) lkllest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A METHOD OF STARTING A FORCED FLOW ONCE-THROUGH VAPOR GENERATORHAVING A FIRST HEATING SECTION INCLUDING VAPOR GENERATING FURNACE WALLSAND HAVING A SECOND HEATING SECTION INCLUDING A PRIMARY SUPERHEATER ANDA FINISHING SUPERHEATER SAID HEATING SECTIONS BEING DIRECTLY CONNECTEDAND BEING SERIALLY ARRANGED FOR FLOW OF A VAPORIZABLE FLUIDTHERETHROUGH; SAID METHOD COMPRISING THE FOLLOWING STEPS: (1)MAINTAINING A BODY OF HEATED WORKING FLUID AT A PREDETERMINED RELATIVELYHIGH PRESSURE IN SAID FIRST HEATING SECTION; (2) FLOWING WORKING FLUIDFROM SAID FIRST HEATING SECTION DIRECTLY TO SAID PRIMARY SUPERHEATER,WHILE REDUCING THE PRESSURE THEREOF FROM SAID HIGH PRESSURE DOWN TO APREDETERMINED LOW PRESSURE MAINTAINED IN SAID PRIMARY SUPERHEATER SAIDLOW PRESSURE BEING SUCH THAT A PARTIAL FLASHING OF SAID FLUID INTO VAPOROCCURS, SO AS TO OBTAIN A BODY OF VAPORIZABLE FLUID AND A BODY OF VAPOR,AND ESTABLISH A FLUID LEVEL IN SAID PRIMARY SUPERHEATER; (3) GENERATINGADDITIONAL VAPOR FROM SAID BODY OF VAPORIZABLE FLUID IN SAID PRIMARYSUPERHEATER AND PASSING VAPOR TO SAID FINISHING SUPERHEATER FORSUPERHEATING THEREIN; (4) CONDUCTING SAID SUPERHEATED VAPOR TO A POINTOF USE; AND (5) CONTROLLING THE FLOW OF VAPORIZABLE FLUID FROM SAIDFIRST HEATING SECTION TO SAID PRIMARY SUPERHEATER TO ESTABLISH ANDMAINTAIN THE FLUID LEVEL IN SAID PRIMARY SUPERHEATER WITHIN DESIREDLIMITS.